The present invention relates to a fuel cell having side thermal insulators used as a thermal insulation mechanism for a fuel cell stack body and which can easily be attached thereto.
A stack body having fuel cell sub-stacks each comprising many cell bodies, i.e., comprising electrolytic plates, anodes, cathodes, separators and so on, generally has side thermal insulators provided on the side thereof, as disclosed in Japanese Patent Laid-Open No. 64-63277. For example, since the working temperatures of a phosphate fuel cell and a fused carbonate fuel cell are 200.degree. C. and 650.degree. C., respectively, the side thermal insulators function to efficiently keep the temperature of a fuel cell body. Particularly, in a fused carbonate fuel cell having a higher working temperature, the thermal insulators are frequently provided on the periphery of a cell stack body and installed in a fuel cell pressure vessel together with mechanical strengthening members such as clamps for the fuel cell.
As shown in FIG. 11, in the conventional fuel cells, the lowermost thermal insulator 50 is placed on a support member 51 placed at the bottom of a stack body 60, and the same thermal insulators 50 are successively stacked on the lowermost thermal insulator 50. The total weight of the insulators is thus supported by the support member 51. Gas supply and exhaust pipes 52, 53 are respectively provided at a plurality of positions of the cell stack body 60, and the pipes 52, 53 must be passed through the side thermal insulators. In addition, since the height of the whole fuel cell stack body 60 repeatedly expands and contracts during operation, the relative position between the pipes 52, 53 and the side thermal insulators 50 varies during operation. Before assembling the cell, a sufficient gap is thus provided in each of the portions of the thermal insulators, through which the pipes 52, 53 are respectively passed, in expectation of contraction of the cell during operation so as to prevent the interference between the pipes 52, 53 and the thermal insulators 50 even if the fuel cell body contracts.
It is thus necessary to previously confirm all portions of interference between the thermal insulators and the fuel cell body and to design the side thermal insulators each having dimensions which cause no interference therebetween. It is also necessary to assemble the fuel cell body in consideration of the procedure of combination with each of the passage portions of the insulators. In order to take the requirements into consideration, conventional side thermal insulators are respectively formed into small elements, which are stacked after a cell is assembled. Since many small elements are stacked, all the elements are not always stacked at the completely same position, and the stack structure is very likely to be unstable.
The height of a fuel cell is increased with an increase in the capacity thereof. The total height of the side thermal insulators for keeping the side of the cell warm is inevitably increased. In a high stacked cell, therefore, a large number of small elements must be stacked high, and high-precision design and careful stacking work are required.
The workload required for constructing the side thermal insulators is extremely large. For example, in the case of a fused carbonate fuel cell, the work of constructing thermal insulators takes about one day even in a cell stack body of a several tens-kW class, and the total workload taken for a large-capacity power plant comprising many cell stack bodies of a several hundreds-kW class installed therein is estimated to be as huge as several months or more. Particularly, in a power plant constructed near a seacoast, if the work of constructing the thermal insulators is performed outdoors, there are the problems that the work is affected by the weather, and that chlorides in air adversely affect the cell sub-stacks during the work of constructing the thermal insulators.
The thermal insulation structure completed as a result of an enormous workload also has the following problems: Since the structure of the side thermal insulators 50 comprising small elements stacked, as described above, there is the danger that when an earthquake occurs during operation of the cell, the thermal insulator assembly itself is disassembled. In addition, the relative relation between the cell side and the side thermal insulator side inevitably depends upon the assembly state of each of the cell stack bodies even if care is taken to design so as to prevent the interference between both sides. As a result, it cannot be said that the fuel cell is constantly operated in a stable state with reliability.